Seed and fertiliser products are distributed from a hopper or aircart to a delivery tool via a pneumatic conveyor tube. The travel path is initially substantially lateral over the first part of the distance from the supply hopper to the delivery tool. Then, the conveyor tube is provided with a substantially vertical orientation and its upper end connects with a flow dividing header. The header directs the air-entrained product into a number of conduits connected with the ground openers and delivery tools. In some cases the conduits of the header communicate with secondary headers before distributing the product to individual delivery tools. It is important to achieve an even distribution of product to each conduit from the header to apply equal amounts of product in each furrow. An uneven distribution results in inefficient soil and fertiliser usage, and affects the uniformity of the produce growth. A term commonly used is the coefficient of variation (CV) which is a measure of the uniformity of distribution across the distribution apparatus. A CV of 15% or greater is deemed unacceptable. A CV below 5% is considered very good.
The variation in distribution is effected by a number of factors. For instance, grain travelling in the conveyor tube tends to travel along the inside surface, particularly following any bend for redirection to vertical. The outlet of the conveyor tube delivers the material to a spreader in the distribution header which separates the material into channels arranged circumferentially about the header. Thus, if the product material is more heavily concentrated at one side of the conveyor tube, distribution will not be even. To deliver the product more evenly into the header, a number of designs have been proposed to create turbulence in the conveyor tube forcing the product away from the inside surface, and to centre the stream of product entering the header.
U.S. Pat. No. 4,717,289 issued to S. Popowich in 1988 discloses a corrugated delivery tube for use with a horizontal distribution head. Corrugations tend to direct material from the side walls in a substantially horizontal system with gravity also affecting the stream. In a substantially vertical orientation, many materials may follow the corrugated surface without experiencing enough turbulence to achieve the desired result.
A vertical header system allows a larger number of separation channels to be arranged circumferentially, without constricting the size of the channels which constriction would increase the pressure requirements and potentially cause more damage to the seed.
Canadian Application No. 2,111,611 to G. Bourgault published in June 1995 discloses the use of a central baffle to divide the material into two streams as it is redirected through a 90 degree bend and centering deflector rings. This is a relatively complicated structure to manufacture. Further, the seed and other material is exposed to a plurality of deflecting surfaces and since they are travelling at high speed this increases the possibility of damaging the seed in particular.
The use of a dimpled distribution tube is disclosed in Canadian Patent 1,167,704 issued to D. Kelm in 1984. A regular pattern of dimples, or interior projections, creates turbulence within the material flow. This design includes a number of variations in an attempt to improve the uniformity of distribution. Both cylindrical and conical tube sections are disclosed having regularly spaced dimples. An alternative embodiment places a dimpled section between two 45 degree bend sections to act on the material more gradually. This design improves the distribution of material considerably over the previous designs. However, the CV results of the Kelm device are somewhat inconsistent depending on the product used and the rate of delivery.
Various product materials, e.g. peas, wheat, canola and fertilisers exhibit different responses to turbulent flow. The objective is to provide a uniform stream of material to the dividing spreader of the header. Since any number and combination of materials may be distributed by the same equipment, it is desirable to find an optimised median system suitable for the full range of products to provide the necessary versatility.
Kelm identified that changing the placement of the dimpled tube section within the conveying system has an effect on the CV from the distribution head. However, it is not practical to reconfigure the conveying system for different products or application conditions.
The distribution head design also has a substantial effect on the CV. The prior art has provided a wide variety of distribution heads. Some heads promote turbulence in the flow while others make attempts to reduce turbulence in the head. Reference may be had to Kelm CA 1,097,149; Weiste AU 437,160; EP 211,295; Wurth SU 1,496,668; Gillespie U.S. Pat. No. 3,189,230; Oberg et al U.S. Pat. No. 4,191,500; Smith et al U.S. Pat. No. 4,413,935; Widmer et al U.S. Pat. No.4,562,968 and Memory CA 2,073,237-A among others. Although several of these designs were partially successful it is the opinion of those skilled in this field that there is room for improvement insofar as effect on CV is concerned.